1. Field of the Invention
The present invention relates to a lamp for a vehicle, the lamp having a projector-type lamp unit.
2. Description of the Background Art
In general, a vehicle lamp is configured in a manner that a lamp unit having an optical axis extending in the longitudinal direction of the vehicle is housed within a lamp chamber, which is formed by a lamp body and a translucent cover attached to the opening portion of the front end of the lamp body. An example of such a lamp unit is a projector-type lamp unit.
In a projector-type lamp of the related art, light emitted from a light source, which converges at a focal point and is diffused radially from the focal point, is projected in the irradiation direction by an aspheric lens, so that the shape of the light distribution pattern has a high degree of freedom, which is advantageous, while the illumination distribution within the light distribution pattern has a low degree of freedom. Thus, there is a problem, for example, that it is difficult to obtain a light distribution pattern that illuminates a distant place brightly. Further, the aspheric lens has a circular shape when seen from the front side thereof, and only the aspheric lens stands out when this lamp is attached to a vehicle. Thus, respective lamps have a similar appearance, so it is impossible to for the respective types of vehicles to have different designs.
In order to solve such problems, Japanese Patent Unexamined Publication JP-A-2003-16813 discloses a projector-type lamp shown in FIG. 7. The projector-type lamp 1 includes a reflecting mirror 2 that is divided into three parts consisting of central reflecting surfaces 2a, 2b formed so as to extend toward the side directions of a light source 3, upper reflecting surfaces 2c, 2d formed at the upper portions of the central reflecting surfaces 2a, 2b, respectively, and lower reflecting surfaces 2e, 2f formed at the lower portions of the central reflecting surfaces 2a, 2b, respectively. A projection lens 4 is formed by an aspherical lens 4a, which is disposed so as to have a focal point near the secondary focal point of the central reflecting surfaces 2a, 2b, and long sideways lenses 4b, 4c, which are disposed at the left and right sides of the aspherical lens 4a, respectively, so that the reflected light from the upper reflecting surfaces 2c, 2d and the reflected light from the lower reflecting surfaces 2e, 2f is incident on the long sideways lenses 4b, 4c, respectively.
Accordingly, illumination characteristics can be obtained so that the brightness in the near area is suppressed, while the distant area is illuminated brightly within the configuration of the light distribution characteristics and so the visibility of the headlamp for the light distribution at the time of running can be improved. Further, since the projection lens is configured by the aspherical lens and the long sideways lenses, the light emission area can be made large, thereby improving the visibility from oncoming vehicles. Furthermore, it becomes possible to have different designs for the different types of vehicles.
However, the projector-type lamp disclosed in JP-A-2003-16813 is configured so that each of the long sideways lenses disposed at the left and right sides of the aspherical lens is a cylindrical lens. Because this cylindrical lens merely diffuses light, it is difficult to control the incident light. In particular, the cylindrical lens can not illuminate direct a desired light distribution from the light source toward a side direction. Therefore, the visibility in the side direction of the road surface cannot be improved sufficiently. Further, since the cylindrical lens has a uniform thickness, the weight thereof is large. Accordingly, the cylindrical lens is disadvantageous in that it has a high cost and is difficult to form. Furthermore, since it is difficult to dispose the cylindrical lens along the tilt of a vehicle body, there is a limited number of different designs that can be used. For example, if the cylindrical lens is forceably fit along the tilt, the entire size of the lamp becomes large and the ability to use different designs is limited.